Humans are not off the hook for extinctions of large herbivores - then or now
(PHYSorg.com Archaeology & Fossils)

What triggered the decline and eventual extinction of many megaherbivores, the giant plant-eating mammals that roamed the Earth millions of years ago, has long been a mystery. These animals, which weighed 1,000kg or more and included the ancient relatives of modern elephants, rhinos, hippos and giraffes, reached a peak of diversity in Africa some 4.5m years ago during the Pliocene epoch (between 5.3m and 2.6m years ago). After this, their numbers slowly declined, in a trend that continued into the Pleistocene (2.6m years ago to roughly 11,000 years ago).